We provide a surface water drainage assessment and design pre-development service which is often combined with a contaminated land investigation, geotechnical investigation and or flood risk assessment. By combining the services there is a potential to save considerable development costs and time.
An understanding of the surface water drainage strategy for a site is required to quantify the risks and potential costs of the development, particularly as any future drainage scheme is likely to require consent from a SuDs Approval Board. It is important to establish the capacity of the sub surface, surface water courses and existing drainage infrastructure to accept the site’s discharge. The presence of any potential contaminant issues will also be considered.
The drainage strategy will incorporate the findings of any of the other elements of the site investigation including the contaminated land assessment and the site geology from available borehole logs. Permeability testing may be required within shallow piezometers, shallow pits or auger holes as appropriate across the site.
The requirement for large surface based attenuation systems will be considered along with the space implications within the site’s footprint. Alternative discharge routes and capacities of surface water courses and sewer systems will be investigated as options. Based on the latest guidelines run-off estimates will be made for a range of potential development land cover (% impermeable area). A Comparison will be made with the existing land cover and drainage system to establish the potential for additional site attenuation requirements to provide a reduction in off-site flood risk and also account for climate change, a methodology sought and preferred by the regulators. A potential drainage strategy will be set out in the context of the local hydrology, hydrogeology and flood risk including the implications of groundwater flooding.
Our consultancy team have provided designs that understand a developers need to limit the space taken up by drainage features whilst keeping the costs of development as realistic as possible.
We have undertaken work for both Developers and Local Authorities including extensive flood risk assessments and drainage plans during the rehabilitation of brownfield sites. Work is undertaken on a range of scales to meet address the risks posed to individual sites.
Bob Sargent is our technical lead on urban development, he has experience of supporting the development of complex sites that have in some cases required Expert Witness level support to gain planning approval.